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Sagittal T1

Degenerative changes of the articular cartilage with thinning and denudation as well as subchondral degenerative change; most evident at the medial tibio-femoral articulation with lateral femoral condyle subchondral 3.5 X 2.7 cm cystic lesion associated with extensive perilesional osseous edema as well as a similar yet much smaller distal femoral intercondylar subarticular cystic lesion. Osteoarthritic changes with subtle marginal osteophytic lipping of the tibio-femoral and patella-femoral articulations.

Mucoid degeneration of the ACL which appears thickened with increased signal intensity alternating with its normal hypointense fibers.

Intact fibers' continuity with normal MR signal of the posterior cruciate and collateral ligaments as well as the quadriceps tendon and patellar ligament.

Moderate knee joint effusion with synovial thickening and frond-like synovial projections with high T1 signal and intermediate to high T2 signal as well as signal suppression in the FAT-suppression sequences.

Lipoma arborescens is idiopathic, however unusual nonspecific reactive response to chronic synovial irritation, either mechanical or inflammatory insults is suggested. It is considered as a lipoma-like benign synovial villous proliferation with replacement of the subsynovial connective tissue by mature fat cells.

The radiological signs are frond-like fat-density or signal intensity synovial lesions (ranging from small frond-like proliferations to large infiltrating fronds of hyperplastic synovium and eventually large rounded or globular fatty mass lesions) usually located within the supra-patellar bursa.

The clinical presentation is usually painless swelling of the knee, with pain later on from accelerated osteoarthritis and internal derangement of the knee.